The objectives of the proposed work are threefold. First, basic research will be carried out to elucidate ways by which the benzene molecule and other aromatic structures can be activated to give chemically reactive species devoid of the special "aromaticity" commonly associated with them. This will be attempted by the synthesis of aromatic rings fused to cyclobutadienoid nuclei designed to significantly reduce aromatic delocalization due to anti-aromatic contributions of the fused ring. Second, saturated strained rings (four and three-rings) will be fused to benzene and other (4n plus 2) II-electronic structures and the effect of strain on II-delocalization investigated. Both classes of compounds will be subjected to the Ames Test. Third, polycyclic hydrocarbons of known mutagenic and carcinogenic (in) activity will be (in)-activated using the above techniques and the effect of this modification monitored by chemical, physical and biochemical analysis. The latter will consist of tests for mutagenic activity and, for the more interesting compounds, also relative carcinogenic potential. In the long-term we hope to provide insights into benzenoid hydrocarbon activation, make a contribution to the theory of aromaticity, and elucidate some of the aspects of the mechanism of hydrocarbon mutagenesis and carcinogenesis.